1. Field of the Invention:
The present invention relates to an improved structure of a connecting end portion of a thin metal tube with a resin tube closely fitted on the periphery along its entire length which has a relatively small diameter of 20 m/m or less and is mainly used as a passage of oil or air in automobiles, various machines, and equipment.
2. Description of the Prior Art:
It is known to use a thin metal tube with a resin tube closely fitted on the periphery along its entire length as a brake pipe, a fuel pipe, or a vacuum pipe for an automobile from the viewpoint of improvement of anticorrosion, reduction in weight of the product, and the readiness of provision. FIG. 2 shows an example of a known connecting end portion structure. A composite tube 11 consists of a thin metal tube 13 and a resin tube 12 closed fitted on the periphery along its entire length. The connecting end portion of the composite tube 11 is provided with a a coaxial and outwardly opening flared portion 14 whose back 15 is directly pressed by the distal end of a nut N' when the nut is threadedly engaged. Reference numeral 16 denotes a neck portion.
With the above-described arrangement of the connecting end portion of the composite tube, since the resin layer on the back surface 15 of the flared portion 14 is directly pressed by the threadedly engaged nut N', that resin layer may be damaged, this often leading to the failure of reuse of the disassembled composite tube. Further, the neck portion 16 may be fatigued by means of torsional stress, resulting in a crack or breakage thereof, if the composite tube is used in a vibrated state.